Texas Math and Science Coaches Association (TMSCA) Science Practice Exam

Studying how seismic waves move through Earth provides a window into its invisible interior. When earthquakes send out waves, their speed and path change as they pass through different layers, and some waves don’t reach certain places at all. The fact that S-waves don’t travel through the outer part of the core reveals that it is liquid, while P-waves bend sharply at the mantle–core boundary, indicating a large, dense layer beneath the mantle. More detailed analysis shows a solid inner core surrounded by a liquid outer core. Magnetic fields, X-rays, and radioactivity don’t give the same direct picture of internal layering, so the core’s structure was first determined primarily from seismic-wave observations.